1. Field of the Invention
This invention relates generally to energy transfer and especially to a heat recovery system for liquid heaters.
In particular, the flue gas energy transfer system of this invention concerns a subsidiary heat off-take for boilers.
2. Background Information
Liquid boilers used for low-pressure steam and hot water installations typically have a pressure vessel divided interiorly into water filed sections, tubes and/or coils. The liquid is separated from a combustion zone by a heating surface. And an oil or gas fired burner produces radiant energy and combustion gases for heating the liquid. The combustion gases are usually exhausted through a flue and discharged into the atmosphere through a chimney.
Various systems have been developed for recuperating heat from exhaust combustion gases. For example, U.S. Pat. No. 6,357,396 describes an apparatus for exchanging heat from the exhaust gas to preheat combustion air. A method for utilizing waste heat for heating room air is discussed in U.S. Pat. No. 4,079,885. U.S. Pat. No. 4,938,172 discloses the use of exhaust gases for supplementary heating of hot water. A heat recovery system wherein furnace exhaust gases are used to transfer heat to water coils is shown in U.S. Pat. No. 4,210,102.
The above systems however, do not provide subsidiary heating directly to the boiler for improving boiler performance.
Briefly, the nature of this invention concerns a flue gas energy transfer system adapted for hydronic boilers. These boilers frequently include a combustion chamber which generates hot gases for heating a fluid medium contained within the boiler. The combustion gases are discharged, usually through a duct network, for release into the atmosphere. The energy transfer system of this invention recovers the waste heat. This is achieved by an arrangement of dampers, within the duct network. The dampers are selectively actuated for redirecting heated exhaust gases through auxiliary ducts placed contiguous to the boiler wherein heat is conductively transferred from the combustion gases to the fluid contained within the boiler. In accordance with the energy transfer system of this invention, the heated exhaust gases can be retained within the auxiliary duct after boiler shutdown to reduce heat loss. The system of this invention also encompasses automated control for sequencing the operation of the boiler.
Having thus summarized the invention, it will be seen that it is a preferred object thereof to provide a flue gas energy transfer system of the general character described herein for improving thermal efficiency of a boiler.
Another preferred object of this invention is to provide a flue gas energy transfer system with increased boiler capacity for higher peak loads.
A still further preferred object of this invention is to provide a flue gas energy transfer system with decreased demand time for reaching optimum operating temperature.
Yet still further preferred object of this invention is to provide a flue gas energy transfer system for maintaining operating temperature for a longer duration after boiler shutdown.
Still yet another object of this invention is to provide a flue gas energy transfer system with reduced stack exit temperatures.
Yet another preferred object of this invention is to provide a flue gas energy transfer system providing for boiler operation at lower draft pressures.